U.S. patent number 6,673,999 [Application Number 10/260,247] was granted by the patent office on 2004-01-06 for magnetically shielded assembly.
This patent grant is currently assigned to Nanoset LLC. Invention is credited to Jeffrey L. Helfer, Stuart G. MacDonald, Xingwu Wang.
United States Patent |
6,673,999 |
Wang , et al. |
January 6, 2004 |
Magnetically shielded assembly
Abstract
A sheath assembly with a magnetic shielding factor of at least
about 0.9 that contains a sheath. The sheath includes nanomagnetic
material, The nanomagnetic material has a mass density of at least
about 0.01 grams per cubic centimeter, a saturation magnetization
of from about 1 to about 36,000 Gauss, a coercive force of from
about 0.01 to about 5,000 Oersteds, a relative magnetic
permeability of from about 1 to about 500,000, and an average
particle size of less than about 100 nanometers.
Inventors: |
Wang; Xingwu (Wellsville,
NY), Helfer; Jeffrey L. (Webster, NY), MacDonald; Stuart
G. (Pultneyville, NY) |
Assignee: |
Nanoset LLC (East Rochester,
NY)
|
Family
ID: |
21990858 |
Appl.
No.: |
10/260,247 |
Filed: |
September 30, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
054407 |
Jan 22, 2002 |
6506972 |
|
|
|
Current U.S.
Class: |
174/36 |
Current CPC
Class: |
B82Y
25/00 (20130101); H01B 11/10 (20130101); H01B
11/1083 (20130101); H01F 10/324 (20130101); A61N
1/3718 (20130101); H01F 1/0063 (20130101); H01F
10/007 (20130101); A61N 1/086 (20170801) |
Current International
Class: |
A61N
1/00 (20060101); A61N 1/16 (20060101); H01B
11/10 (20060101); H01F 10/00 (20060101); H01B
11/02 (20060101); H01F 10/32 (20060101); H01B
7/04 (20060101); H01B 011/06 () |
Field of
Search: |
;174/36,12SC
;333/12,243 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Nguyen; Chau N.
Attorney, Agent or Firm: Greenwald; Howard J.
Parent Case Text
REFERENCE TO RELATED PATENT APPLICATION
This application is a continuation-in-part of applicant's copending
patent application U.S. Ser. No. 10/054,407, filed on Jan. 22, 2002
now U.S. Pat. No. 6,506,972.
Claims
We claim:
1. A sheath assembly with a magnetic shielding factor of at least
about 0.9, wherein said sheath assembly is comprised of a sheath,
wherein said sheath is comprised of nanomagnetic material, and
wherein said nanomagnetic material has a mass density of at least
about 0.01 grams per cubic centimeter, a saturation magnetization
of from about 1 to about 36,000 Gauss, a coercive force of from
about 0.01 to about 5,000 Oersteds, a relative magnetic
permeability of from about 1 to about 500,000, and an average
particle size of less than about 100 nanometers.
2. The sheath assembly as recited in claim 1, wherein said
nanomagnetic material is comprised of nanomagnetic liquid crystal
material.
3. The sheath assembly as recited in claim 2, wherein said sheath
is comprised of a first multiplicity of liquid crystals disposed
within a matrix.
4. The sheath assembly as recited in claim 3, wherein said liquid
crystals are comprised of said nanomagnetic material.
5. The sheath assembly as recited in claim 4, wherein said
multiplicity of liquid crystals are comprised of a first liquid
crystal composition and a second liquid crystal composition.
6. The sheath assembly as recited in claim 5, wherein said first
liquid crystal composition is present in said sheath at a
concentration different than the concentration that said second
liquid crystal composition is present in said sheath.
7. The sheath assembly as recited in claim 6, wherein the physical
properties of said first liquid crystal composition differs from
the physical properties of said second liquid crystal
composition.
8. The sheath assembly as recited in claim 1, wherein said
nanomagnetic material is disposed on the inside surface of said
sheath.
9. The sheath assembly as recited in claim 1, further comprising a
medical device disposed within said sheath.
10. The sheath assembly as recited in claim 9, wherein said sheath
is contiguous with said medical device.
11. The sheath assembly as recited 1, wherein said sheath is
comprised of heat shrinkable material.
12. The sheath assembly as recited in claim 1, wherein said sheath
is comprised of a tearable seam.
13. The sheath assembly as recited in claim 1, wherein said sheath
is comprised of an external surface, and wherein said external
surface is comprised of at least about 50 percent of said
nanomagnetic material.
14. The sheath assembly as recited in claim 1, wherein said sheath
is comprised of an internal surface, and wherein said nanomagnetic
material comprises at least 50 percent of said internal
surface.
15. The sheath assembly as recited in claim 1, wherein said sheath
is a collapsible tube.
16. The sheath assembly as recited in claim 1, wherein said sheath
is a rigid tube.
17. The sheath assembly as recited in claim 1, wherein said sheath
is a flexible tube.
18. The sheath assembly as recited in claim 1, wherein said sheath
is comprised of a first layer of said nanomagnetic material, and a
second layer of said nanomagnetic material, provided that the
magnetic properties of said first layer of nanomagnetic material
differ from the magnetic properties of said second layer of
nanomagnetic material.
19. The sheath assembly as recited in claim 18, wherein said first
layer of nanomagnetic material is contiguous with said second layer
of nanomagnetic material.
20. The sheath assembly as recited in claim 18, wherein said first
layer of nanomagnetic material is not contiguous with said second
layer of nanomagnetic material.
21. The sheath assembly as recited in claim 18, wherein said first
layer of nanomagnetic material has a first thermal conductivity of
from about 10 to about 2,000 calories-centimeter per hour per
square centimeter per degree Celsius, and said second layer of
nanomagnetic material has a second thermal conductivity of from
about 0.2 to about 10 calories-centimeter per hour per square
centimeter per degree Celsius.
22. The sheath assembly as recited in claim 21, wherein said first
layer of nanomagnetic material has a thermal conductivity that is
at least about 10 to about 1000 times higher than the thermal
conductivity of said second layer of nanomagnetic material.
23. The sheath assembly as recited in claim 1, wherein said sheath
assembly is disposed within a living organism.
24. The sheath assembly as recited in claim 1, wherein said sheath
assembly is comprised of a power source.
25. The sheath assembly as recited in claim 24, wherein said power
source provides alternating current.
26. The sheath assembly as recited in claim 24, wherein said power
source provides direct current.
27. The sheath assembly as recited in claim 1, wherein said
nanomagnetic material is comprised of nano-sized ferrites.
28. The sheath assembly as recited in claim 1, wherein said sheath
is comprised of an insulating matrix within which said nanomagnetic
material is disposed.
29. The sheath assembly as recited in claim 1, wherein said sheath
is comprised of a layer of insulating material, and wherein said
nanomagnetic material is contiguous with said layer of insulating
material.
30. The sheath assembly as recited in claim 1, wherein said sheath
assembly is comprised of an exterior surface and an interior
surface, and wherein said nanomagnetic material is disposed on each
of said exterior surface and said interior surface.
31. The sheath assembly as recited in claim 1, wherein said sheath
has a cylindrical shape.
32. The sheath assembly as recited in claim 31, further comprising
a helical member disposed within said sheath.
33. The sheath assembly as recited in claim 32, wherein said
helical member is coated with said nanomagnetic material.
34. The sheath assembly as recited in claim 31, wherein a first
layer of nanomagnetic material is disposed around said sheath.
35. The sheath assembly as recited in claim 34, wherein a second
layer of nanomagnetic material is disposed around said first layer
of nanomagnetic material.
36. The sheath assembly as recited in claim 35, wherein said second
layer of nanomagnetic material has a thickness which differs from
the thickness of said first layer of nanomagnetic material.
37. The sheath assembly as recited in claim 1, wherein said
nanomagnetic material has an average particle size of from about 2
to about 50 nanometers.
38. The sheath assembly as recited in claim 1, further comprising a
first sensor.
39. The sheath assembly as recited in claim 38, wherein said first
sensor is a temperature sensor.
40. The sheath assembly as recited in claim 38, wherein said first
sensor is a magnetic field strength sensor.
41. The sheath assembly as recited in claim 38, further comprising
a second sensor.
42. The sheath assembly as recited in claim 1, further comprising
means of delivering electromagnetic energy to said sheath.
43. The sheath assembly as recited in claim 1, wherein said sheath
is comprised of an internal hollow lumen.
Description
FIELD OF THE INVENTION
A magnetically shielded sheath assembly comprised of a sheath
containing nanomagnetic material that is attached to a device to be
shielded.
BACKGROUND OF THE INVENTION
Many implanted medical devices that are powered by electrical
energy have been developed. Most of these devices comprise a power
source, one or more conductors, and a load.
When a patient with one of these implanted devices is subjected to
high intensity magnetic fields, currents are often induced in the
implanted conductors. The large current flows so induced often
create substantial amounts of heat. Because living organisms can
generally only survive within a relatively narrow range of
temperatures, these large current flows are dangerous.
Furthermore, implantable devices, such as implantable pulse
generators (IPGs) and cardioverter/defibrillator/pacemaker (CDPs),
are sensitive to a variety of forms of electromagnetic interference
(EMI). These devices include sensing and logic systems that respond
to low-level signals from the heart. Because the sensing systems
and conductive elements of these implantable devices are responsive
to changes in local electromagnetic fields, they are vulnerable to
external sources of severe electromagnetic noise, and in particular
to electromagnetic fields emitted during magnetic resonance imaging
(MRI) procedures. Therefore, patients with implantable devices are
generally advised not to undergo magnetic resonance imaging (MRI)
procedures, which often generate static magnetic fields of from
between about 0.5 to about 10 Teslas and corresponding time-varying
magnetic fields of about 20 megahertz to about 430 megahertz, as
dictated by the Lamor frequency (see, e.g., page 1007 of Joseph D.
Bronzino's "The Biomedical Engineering Handbook," CRC Press,
Hartford, Connecticut, 1995). Typically, the strength of the
magnetic component of such a time-varying magnetic field is about 1
to about 1,000 micro Tesla.
One additional problem with implanted conductors is that, when they
are conducting electricity and are simultaneously subjected to
large magnetic fields, a Lorentz force is created which often
causes the conductor to move. This movement may damage body
tissue.
In U.S. Pat. No. 4,180,600, there is disclosed and claimed a fine
magnetically shielded conductor wire consisting of a conductive
copper core and a magnetically soft alloy metallic sheath
metallurgically secured to the conductive core, wherein the sheath
consists essentially of from 2 to 5 weight percent of molybdenum,
from about 15 to about 23 weight percent of iron, and from about 75
to about 85 weight percent of nickel. Although the device of this
patent does provide magnetic shielding, it still creates heat when
it interacts with strong magnetic fields.
It is an object of this invention to provide a sheath assembly,
which is shielded from magnetic fields.
SUMMARY OF THE INVENTION
In accordance with this invention, there is provided a magnetically
shielded sheath assembly comprised of a sheath and nanomagnetic
material. The nanomagnetic material comprises nanomagnetic
particles, and these nanomagnetic particles respond to an
externally applied magnetic field by realigning to the externally
applied field.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described by reference to the following
drawings, in which like numerals refer to like elements, and in
which:
FIG. 1 is a schematic sectional view of a shielded implanted device
comprised of one preferred conductor assembly of the invention;
FIG. 1A is a flow diagram of a preferred process of the
invention;
FIG. 2 is an enlarged sectional view of a portion of the conductor
assembly of FIG. 1;
FIG. 3 is a sectional view of another conductor assembly of this
invention;
FIG. 4 is a schematic view of the conductor assembly of FIG. 2;
FIG. 5 is a sectional view of the conductor assembly of FIG. 2;
FIG. 6 is a schematic of another preferred shielded conductor
assembly;
FIG. 7 is a schematic of yet another configuration of a shielded
conductor assembly;
FIGS. 8A, 8B, 8C, and 8D are schematic sectional views of a
substrate, such as one of the specific medical devices described in
this application, coated with nanomagnetic particulate matter on
its exterior surface;
FIG. 9 is a schematic sectional view of an elongated cylinder,
similar to the specific medical devices described in this
application, coated with nanomagnetic particulate (the cylinder
encloses a flexible, expandable helical member, which is also
coated with nanomagnetic particulate material);
FIG. 10 is a flow diagram of a preferred process of the
invention;
FIG. 11 is a schematic sectional view of a substrate, similar to
the specific medical devices described in this application, coated
with two different populations of elongated nanomagnetic
particulate material;
FIG. 12 is a schematic sectional view of an elongated cylinder,
similar to the specific medical devices described in this
application, coated with nanomagnetic particulate, wherein the
cylinder includes a channel for active circulation of a heat
dissipation fluid;
FIGS. 13A, 13B, and 13C are schematic views of an implantable
catheter coated with nanomagnetic particulate material;
FIGS. 14A through 14G are schematic views of an implantable,
steerable catheter coated with nanomagnetic particulate
material;
FIGS. 15A, 15B and 15C are schematic views of an implantable guide
wire coated with nanomagnetic particulate material;
FIGS. 16A and 16B are schematic views of an implantable stent
coated with nanomagnetic particulate material;
FIG. 17 is a schematic view of a biopsy probe coated with
nanomagnetic particulate material;
FIGS. 18A and 18B are schematic views of a tube of an endoscope
coated with nanomagnetic particulate material;
FIGS. 19A and 19B are schematics f one embodiment of the
magnetically shielding assembly of this invention;
FIGS. 20A, 20B, 20C, 20D, 20E, and 20F are enlarged sectional views
of a portion of a shielding assembly illustrating nonaligned and
magnetically aligned nanomagnetic liquid crystal materials in
different configurations;
FIG. 21 is a graph showing the relationship of the alignment of the
nanomagnetic liquid crystal material of FIGS. 20A and 20B with
magnetic field strength;
FIG. 22 is a graph showing the relationship of the attenuation
provided by the shielding device of this invention as a function of
frequency of the applied magnetic field;
FIG. 23 is a flow diagram of one preferred process for preparing
the nanomagnetic liquid crystal compositions of this invention;
FIG. 24 is a sectional view of a multiplayer structure comprised of
different nanomagnetic materials;
FIG. 25 is a sectional view of another multilayer structure
comprised of different nanomagnetic materials and an electrical
insulating layer.
FIG. 26 is a schematic view of yet another multilayer structure
comprised of nanomagnetic material;
FIG. 27 is a schematic of yet another multilayer structure
comprised of nanomagnetic material; and
FIG. 28 is a schematic of yet another multiplayer structure
comprised of nanomagnetic material.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a schematic sectional view of one preferred device 10
that, in one embodiment, is implanted in a living organism.
Referring to FIG. 1, it will be seen that device 10 is comprised of
a power source 12, a first conductor 14, a second conductor 16, a
first insulative shield 18 disposed about power source 12, a second
insulative shield 20 disposed about a load 22, a third insulative
shield 23 disposed about a first conductor 14, and a second
conductor 16, and a multiplicity of nanomagentic particles 24
disposed on said first insulative shield, said second insulative
shield, and said third insulative shield.
In the embodiment depicted in FIG. 1, the power source 12 is a
battery 12 that is operatively connected to a controller 26. In the
embodiment depicted, controller 26 is operatively connected to the
load 22 and the switch 28. Depending upon the information furnished
to controller 26, it may deliver no current, direct current, and/or
current pulses to the load 22.
In one embodiment, not shown, the controller 26 and/or the wires 30
and 32 are shielded from magnetic radiation. In another embodiment,
not shown, one or more connections between the controller 26 and
the switch 28 and/or the load 22 are made by wireless means such
as, e.g., telemetry means.
In one embodiment, not shown, the power source 12 provides a source
of alternating current. In another embodiment, the power source 12
in conjunction with the controller 26 provides pulsed direct
current.
The load 22 may be any of the implanted devices known to those
skilled in the art. Thus, e.g., load 22 may be a pacemaker. Thus,
e.g., load 22 may be an artificial heart. Thus, e.g., load 22 may
be a heart-massaging device. Thus, e.g., load 22 may be a
defibrillator.
The conductors 14 and 16 may be any conductive material(s) that
have a resistivity at 20 degrees Centigrade of from about 1 to
about 100 microohm-centimeters. Thus, e.g., the conductive
material(s) may be silver, copper, aluminum, alloys thereof,
mixtures thereof, and the like.
In one embodiment, the conductors 14 and 16 consist essentially of
such conductive material. Thus, e.g., it is preferred not to use,
e.g., copper wire coated with enamel. The use of such typical
enamel coating on the conductor does not work well in the instant
invention.
In the first step of the process of this invention, step 40, the
conductive wires 14 and 16 are coated with electrically insulative
material. Suitable insulative materials include nano-sized silicon
dioxide, aluminum oxide, cerium oxide, yttrium-stabilized zirconia,
silicon carbide, silicon nitride, aluminum nitride, and the like.
In general, these nano-sized particles will have a particle size
distribution such that at least about 90 weight percent of the
particles have a maximum dimension in the range of from about 10 to
about 100 nanometers.
The coated conductors 14 and 16 may be prepared by conventional
means such as, e.g., the process described in U.S. Pat. No.
5,540,959, the entire disclosure of which is hereby incorporated by
reference into this specification. This patent describes and claims
a process for preparing a coated substrate, comprising the steps
of: (a) creating mist particles from a liquid, wherein: 1. said
liquid is selected from the group consisting of a solution, a
slurry, and mixtures thereof, 2. said liquid is comprised of
solvent and from 0.1 to 75 grams of solid material per liter of
solvent, 3. at least 95 volume percent of said mist particles have
a maximum dimension less than 100 microns, and 4. said mist
particles are created from said first liquid at a rate of from 0.1
to 30 milliliters of liquid per minute; (b) contacting said mist
particles with a carrier gas at a pressure of from 761 to 810
millimeters of mercury; (c) thereafter contacting said mist
particles with alternating current radio frequency energy with a
frequency of at least 1 megahertz and a power of at least 3
kilowatts while heating said mist particles to a temperature of at
least about 100 degrees centigrade, thereby producing a heated
vapor; (d) depositing said heated vapor onto a substrate, thereby
producing a coated substrate; and (e) subjecting said coated
substrate to a temperature of from about 450 to about 1,400 degrees
centigrade for at least about 10 minutes.
By way of further illustration, one may coat conductors 14 and 16
by means of the processes disclosed in a text by D. Satas on
"Coatings Technology Handbook" (Marcel Dekker, Inc., New York,
N.Y., 1991). As is disclosed in such text, one may use cathodic arc
plasma deposition (see pages 229 et seq.), chemical vapor
deposition (see pages 257 et seq.), sol-gel coatings (see pages 655
et seq.), and the like.
FIG. 2 is a sectional view of the coated conductors 14/16 of the
device of FIG. 1. Referring to FIG. 2, it will be seen that
conductors 14 and 16 are separated by insulating material 42. In
order to obtain the structure depicted in FIG. 2, one may
simultaneously coat conductors 14 and 16 with the insulating
material so that such insulators both coat the conductors 14 and 16
and fill in the distance between them with insulation.
The insulating material 42 that is disposed between conductors
14/16, may be the same as the insulating material 44/46 that is
disposed above conductor 14 and below conductor 16. Alternatively,
and as dictated by the choice of processing steps and materials,
the insulating material 42 may be different from the insulating
material 44 and/or the insulating material 46. Thus, step 48 of the
process describes disposing insulating material between the coated
conductors 14 and 16. This step may be done simultaneously with
step 40; and it may be done thereafter.
The insulating material 42, the insulating material 44, and the
insulating material 46 each generally has a resistivity of from
about 1,000,000,000 to about 10,000,000,000,000
ohm-centimeters.
After the insulating material 42/44/46 has been deposited, and in
one embodiment, the coated conductor assembly is preferably heat
treated in step 50. This heat treatment often is used in
conjunction with coating processes in which the heat is required to
bond the insulative material to the conductors 14/16.
The heat-treatment step may be conducted after the deposition of
the insulating material 42/44/46, or it may be conducted
simultaneously therewith. In either event, and when it is used, it
is preferred to heat the coated conductors 14/16 to a temperature
of from about 200 to about 600 degrees Centigrade for from about 1
minute to about 10 minutes.
Referring again to FIG. 1A, and in step 52 of the process, after
the coated conductors 14/16 have been subjected to heat treatment
step 50, they are allowed to cool to a temperature of from about 30
to about 100 degrees Centigrade over a period of time of from about
3 to about 15 minutes.
One need not invariably heat treat and/or cool. Thus, referring to
FIG. 1A, one may immediately coat nanomagnetic particles onto to
the coated conductors 14/16 in step 54 either after step 48 and/or
after step 50 and/or after step 52.
In step 54, nanomagnetic materials are coated onto the previously
coated conductors 14 and 16. This is best shown in FIG. 2, wherein
the nanomagnetic particles are identified as particles 24.
In general, and as is known to those skilled in the art,
nanomagnetic material is magnetic material which has an average
particle size less than 100 nanometers and, preferably, in the
range of from about 2 to 50 nanometers. Reference may be had, e.g.,
to U.S. Pat. No. 5,889,091 (rotationally free nanomagnetic
material), U.S. Pat. Nos. 5,714,136, 5,667,924, and the like. The
entire disclosure of each of these United States patents is hereby
incorporated by reference into this specification.
The nanomagnetic materials may be, e.g., nano-sized ferrites such
as, e.g., the nanomagnetic ferrites disclosed in U.S. Pat. No.
5,213,851, the entire disclosure of which is hereby incorporated by
reference into this specification. This patent claims a process for
coating a layer of ferritic material with a thickness of from about
0.1 to about 500 microns onto a substrate at a deposition rate of
from about 0.01 to about 10 microns per minute per 35 square
centimeters of substrate surface, comprising the steps of: (a)
providing a solution comprised of a first compound and a second
compound, wherein said first compound is an iron compound and said
second compound is selected from the group consisting of compounds
of nickel, zinc, magnesium, strontium, barium, manganese, lithium,
lanthanum, yttrium, scandium, samarium, europium, terbium,
dysprosium, holmium, erbium, ytterbium, lutetium, cerium,
praseodymium, thulium, neodymium, gadolinium, aluminum, iridium,
lead, chromium, gallium, indium, chromium, samarium, cobalt,
titanium, and mixtures thereof, and wherein said solution is
comprised of from about 0.01 to about 1,000 grams of a mixture
consisting essentially of said compounds per liter of said
solution; (b) subjecting said solution to ultrasonic sound waves at
a frequency in excess of 20,000 hertz, and to an atmospheric
pressure of at least about 600 millimeters of mercury, thereby
causing said solution to form into an aerosol; (c) providing a
radio frequency plasma reactor comprised of a top section, a bottom
section, and a radio-frequency coil; (d) generating a hot plasma
gas within said radio frequency plasma reactor, thereby producing a
plasma region; (e) providing a flame region disposed above said top
section of said radio frequency plasma reactor; (f) contacting said
aerosol with said hot plasma gas within said plasma reactor while
subjecting said aerosol to an atmospheric pressure of at least
about 600 millimeters of mercury and to a radio frequency
alternating current at a frequency of from about 100 kilohertz to
about 30 megahertz, thereby forming a vapor; (g) providing a
substrate disposed above said flame region; and (h) contacting said
vapor with said substrate, thereby forming said layer of ferritic
material.
By way of further illustration, one may use the techniques
described in an article by M. De Marco, X. W. Wang, et al. on
"Mossbauer and magnetization studies of nickel ferrites" published
in the Journal of Applied Physics 73(10), May 15, 1993, at pages
6287-6289.
In general, the thickness of the layer of nanomagnetic material
deposited onto the coated conductors 14/16 is less than about 5
microns and generally from about 0.1 to about 3 microns.
After the nanomagnetic material is coated in step 54, the coated
assembly may be optionally heat-treated in step 56. In this
optional step 56, it is preferred to subject the coated conductors
14/16 to a temperature of from about 200 to about 600 degrees
Centigrade for from about 1 to about 10 minutes.
In one embodiment, illustrated in FIG. 3, one or more additional
insulating layers 43 are coated onto the assembly depicted in FIG.
2, by one or more of the processes disclosed hereinabove. This is
conducted in optional step 58 (see FIG. 1A).
FIG. 4 is a partial schematic view of the assembly 11 of FIG. 2,
illustrating the current flow in such assembly. Referring go FIG.
4, it will be seen that current flows into conductor 14 in the
direction of arrow 60, and it flows out of conductor 16 in the
direction of arrow 62. The net current flow through the assembly 11
is zero; and the net Lorentz force in the assembly 11 is thus zero.
Consequently, even high current flows in the assembly 11 do not
cause such assembly to move.
In the embodiment depicted in FIG. 4, conductors 14 and 16 are
substantially parallel to each other. As will be apparent, without
such parallel orientation, there may be some net current and some
net Lorentz effect.
In the embodiment depicted in FIG. 4, and in one preferred aspect
thereof, the conductors 14 and 16 preferably have the same
diameters and/or the same compositions and/or the same length.
Referring again to FIG. 4, the nanomagnetic particles 24 are
present in a density sufficient so as to provide shielding from
magnetic flux lines 64. Without wishing to be bound to any
particular theory, applicant believes that the nanomagnetic
particles 24 trap and pin the magnetic lines of flux 64.
In order to function optimally, the nanomagnetic particles 24 have
a specified magnetization. As is known to those skilled in the art,
magnetization is the magnetic moment per unit volume of a
substance. Reference may be had, e.g., to U.S. Pat. Nos. 4,169,998,
4,168,481, 4,166,263, 5,260,132, 4,778,714, and the like. The
entire disclosure of each of these United States patents is hereby
incorporated by reference into this specification.
Referring again to FIG. 4, the layer of nanomagnetic particles 24
preferably has a saturation magnetization, at 25 degrees
Centigrade, of from about 1 to about 36,000 Gauss, or higher. In
one embodiment, the saturation magnetization at room temperature of
the nanomagentic particles is from about 500 to about 10,000 Gauss.
For a discussion of the saturation magnetization of various
materials, reference may be had, e.g., to U.S. Pat. Nos. 4,705,613,
4,631,613, 5,543,070, 3,901,741 (cobalt, samarium, and gadolinium
alloys), and the like. The entire disclosure of each of these
United States patents is hereby incorporated by reference into this
specification. As will be apparent to those skilled in the art,
especially upon studying the aforementioned patents, the saturation
magnetization of thin films is often higher than the saturation
magnetization of bulk objects.
In one embodiment, it is preferred to utilize a thin film with a
thickness of less than about 2 microns and a saturation
magnetization in excess of 20,000 Gauss. The thickness of the layer
of nanomagentic material is measured from the bottom surface of the
layer that contains such material to the top surface of such layer
that contains such material; and such bottom surface and/or such
top surface may be contiguous with other layers of material (such
as insulating material) that do not contain nanomagnetic
particles.
Thus, e.g., one may make a thin film in accordance with the
procedure described at page 156 of Nature, Volume 407, Sep. 14,
2000, that describes a multilayer thin film has a saturation
magnetization of 24,000 Gauss.
By the appropriate selection of nanomagnetic particles, and the
thickness of the films deposited, one may obtain saturation
magnetizations of as high as at least about 36,000.
In the preferred embodiment depicted in FIG. 4, the nanomagnetic
particles 24 are disposed within an insulating matrix so that any
heat produced by such particles will be slowly dispersed within
such matrix. Such matrix, as indicated hereinabove, may be made
from ceria, calcium oxide, silica, alumina. In general, the
insulating material 42 preferably has a thermal conductivity of
less than about 20 (caloriescentimeters/square centimeters--degree
second).times.10,000. See, e.g., page E-6 of the 63.sup.rd Edition
of the "Handbook of Chemistry and Physics" (CRC Press, Inc., Boca
Raton, Fla., 1982).
The nanomagnetic materials 24 typically comprise one or more of
iron, cobalt, nickel, gadolinium, and samarium atoms. Thus, e.g.,
typical nanomagnetic materials include alloys of iron and nickel
(permalloy), cobalt, niobium, and zirconium (CNZ), iron, boron, and
nitrogen, cobalt, iron, boron, and silica, iron, cobalt, boron, and
fluoride, and the like. These and other materials are descried in a
book by J. Douglas Adam et al. entitled "Handbook of Thin Film
Devices" (Academic Press, San Diego, Calif., 2000). Chapter 5 of
this book beginning at page 185, describes "magnetic films for
planar inductive components and devices;" and Tables 5.1 and 5.2 in
this chapter describe many magnetic materials.
FIG. 5 is a sectional view of the assembly 11 of FIG. 2. The device
of FIG. 5, and of the other Figures of this application, is
preferably substantially flexible. As used in this specification,
the term flexible refers to an assembly that can be bent to form a
circle with a radius of less than 2 centimeters without breaking.
Put another way, the bend radius of the coated assembly 11 can be
less than 2 centimeters. Reference may be had, e.g., to U.S. Pat.
Nos. 4,705,353, 5,946,439, 5,315,365, 4,641,917, 5,913,005, and the
like. The entire disclosure of each of these United States patents
is hereby incorporated by reference into this specification.
In another embodiment, not shown, the shield is not flexible. Thus,
in one aspect o f this embodiment, the shield is a rigid, removable
sheath that can be placed over an endoscope or a biopsy probe used
inter-operatively with magnetic resonance imaging.
As will be apparent, even when the magnetic insulating properties
of the assembly of this invention are not 100 percent effective,
the assembly still prevents the rapid dissipation of heat to bodily
tissue.
In another embodiment of the invention, there is provided a
magnetically shielded conductor assembly comprised of a conductor
and a film of nanomagnetic material disposed above said conductor.
In this embodiment, the conductor has a resistivity at 20 degrees
Centigrade of from about 1 to about 2,000 micro ohm-centimeters and
is comprised of a first surface exposed to electromagnetic
radiation. In this embodiment, the film of nanomagnetic material
has a thickness of from about 100 nanometers to about 10
micrometers and a mass density of at least about about 1 gram per
cubic centimeter, wherein the film of nanomagnetic material is
disposed above at least about 50 percent of said first surface
exposed to electromagnetic radiation, and the film of nanomagnetic
material has a saturation magnetization of from about 1 to about
36,000 Gauss, a coercive force of from about 0.01to about 5,000
Oersteds, a relative magnetic permeability of from about 1 to about
500,000, and a magnetic shielding factor of at least about 0.5. In
this embodiment, the nanomagnetic material has an average particle
size of less than about 100 nanometers.
In the preferred embodiment of this invention, a film of
nanomagnetic is disposed above at least one surface of a conductor.
Referring to FIG. 6, and in the schematic diagram depicted therein,
a source of electromagnetic radiation 100 emits radiation 102 in
the direction of film 104. Film 104 is disposed above conductor
106, i.e., it is disposed between conductor 106 of the
electromagnetic radiation 102.
The film 104 is adapted to reduce the magnetic field strength at
point 108 (which is disposed less than 1 centimeter above film 104)
by at least about 50 percent. Thus, if one were to measure the
magnetic field strength at point 108, and thereafter measure the
magnetic field strength at point 110 (which is disposed less than 1
centimeter below film 104), the latter magnetic field strength
would be no more than about 50 percent of the former magnetic field
strength. Put another way, the film 104 has a magnetic shielding
factor of at least about 0.5.
In one embodiment, the film 104 has a magnetic shielding factor of
at least about 0.9, i.e., the magnetic field strength at point 110
is no greater than about 10 percent of the magnetic field strength
at point 108. Thus, e.g., the static magnetic field strength at
point 108 can be, e.g., one Tesla, whereas the static magnetic
field strength at point 110 can be, e.g., 0.1 Tesla. Furthermore,
the time-varying magnetic field strength of a 100 milliTesla would
be reduced to about 10 milliTesla of the time-varying field.
Referring again to FIG. 6, the nanomagnetic material 103 in film
104 has a saturation magnetization of form about 1 to about 36,000
Gauss. This property has been discussed elsewhere in this
specification. In one embodiment, the nanomagnetic material 103 a
saturation magnetization of from about 200 to about 26,000
Gauss.
The nanomagnetic material 103 in film 104 also has a coercive force
of from about 0.01 to about 5,000 Oersteds. The term coercive force
refers to the magnetic field, H, which must be applied to a
magnetic material in a symmetrical, cyclicly magnetized fashion, to
make the magnetic induction, B, vanish; this term often is referred
to as magnetic coercive force. Reference may be had, e.g., to U.S.
Pat. Nos. 4,061,824, 6,257,512, 5,967,223, 4,939,610, 4,741,953,
and the like. The entire disclosure of each of these United States
patents is hereby incorporated by reference into this
specification.
In one embodiment, the nanomagnetic material 103 has a coercive
force of from about 0.01 to about 3,000 Oersteds. In yet another
embodiment, the nanomagnetic material 103 has a coercive force of
from about 0.1 to about 10.
Referring again to FIG. 6, the nanomagnetic material 103 in film
104 preferably has a relative magnetic permeability of from about 1
to about 500,000; in one embodiment, such material 103 has a
relative magnetic permeability of from about 1.5 to about 260,000.
As used in this specification, the term relative magnetic
permeability is equal to B/H, and is also equal to the slope of a
section of the magnetization curve of the film. Reference may be
had, e.g., to page 4-28 of E. U. Condon et al.'s "Handbook of
Physics" (McGraw-Hill Book Company, Inc., New York, 1958).
Reference also may be had to page 1399 of Sybil P. Parker's
"McGraw-Hill Dictionrary of Scientific and Technical Terms," Fourth
Edition (McGraw Hill Book Company, New York, 1989). As is disclosed
on this page 1399, permeability is " . . . a factor, characteristic
of a material, that is proportional to the magnetic induction
produced in a material divided by the magnetic field strength; it
is a tensor when these quantities are not parallel.
Reference also may be had, e.g., to U.S. Pat. Nos. 6,181,232,
5,581,224, 5,506,559, 4,246,586, 6,390,443, and the like. The
entire disclosure of each of these United States patents is hereby
incorporated by reference into this specification.
In one embodiment, the nanomagnetic material 103 in film 104 has a
relative magnetic permeability of from about 1.5 to about
2,000.
Referring again to FIG. 6, the nanomagnetic material 103 in film
104 preferably has a mass density of at least about 0.001 grams-per
cubic centimeter; in one embodiment, such mass density is at least
about 1 gram per cubic centimeter. As used in this specification,
the term mass density refers to the mass of a give substance per
unit volume. See, e.g., page 510 of the aforementioned "McGraw-Hill
Dictionary of Scientific and Technical Terms." In one embodiment,
the film 104 has a mass density of at least about 3 grains per
cubic centimeter. In another embodiment, the nanomagnetic material
103 has a mass density of at least about 4 grams per cubic
centimeter.
In the embodiment depicted in FIG. 6, the film 104 is disposed
above 100 percent of the surfaces 112, 114, 116, and 118 of the
conductor 106. In the embodiment depicted in FIG. 2, by comparison,
the nanomagnetic film is disposed around the conductor.
Yet another embodiment is depicted in FIG. 7. In the embodiment
depicted in FIG. 7, the film 104 is not disposed in front of either
surface 114, or 116, or 118 of the conductor 106. Inasmuch as
radiation is not directed towards these surfaces, this is
possible.
What is essential, however, is that the film 104 be interposed
between the radiation 102 and surface 112. It is preferred that
film 104 be disposed above at least about 50 percent of surface
112. In one embodiment, film 104 is disposed above at least about
90 percent of surface 112.
In the remainder of this specification, the use of film 104 with
various medical devices will be discussed.
Many implanted medical devices have been developed to help medical
practitioners treat a variety of medical conditions by introducing
an implantable medical device, partly or completely, temporarily or
permanently, into the esophagus, trachea, colon, biliary tract,
urinary tract, vascular system or other location within a human or
veterinary patient. For example, many treatments of the vascular
system entail the introduction of a device such as a guidewire,
catheter, stent, arteriovenous shunt, angioplasty balloon, a
cannula or the like. Other examples of implantable medical devices
include, e.g., endoscopes, biopsy probes, wound drains,
laparoscopic equipment, urethral inserts, and implants. Most such
implantable medical devices are made in whole or in part of metal,
and are not part of an electrical circuit.
When a patient with one of these implanted devices is subjected to
high intensity magnetic fields, such as during magnetic resonance
imaging (MRI), electrical currents are induced in the metallic
portions of the implanted devices. The electrical currents so
induced often create substantial amounts of heat. The heat can
cause extensive damage to the tissue surrounding the implantable
medical device.
Furthermore, when a patient with one of these implanted devices
undergoes MRI, signal loss and disruption the diagnostic image
often occur as a result of the presence of a metallic object, which
causes a disruption of the local magnetic field. This disruption of
the local magnetic field alters the relationship between position
and frequency, which are crucial for proper image reconstruction.
Therefore, patients with implantable medical devices are generally
advised not to undergo MRI procedures. In many cases, the presence
of such a device is a strict contraindication for MRI (See
Shellock, F. G., Magnetic Resonance Procedures: Health Effects and
Safety, 2001 Edition, CRC Press, Boca Raton, Fla., and Food and
Drug Administration, Magnetic Resonance Diagnostic Device: Panel
Recommendation and Report on Petitions for MR Reclassification,
Federal register, 1988, 53, 7575-7579). Any contraindication such
as this, whether a strict or relative contraindication, is serious
problem since it deprives the patient from undergoing an MRI
examination, or even using MRI to guide other therapies, such as
proper placement of diagnostic and/or therapeutics devices
including angioplasty balloons, RF ablation catheters for treatment
of cardiac arrythmias, sensors to assess the status of
pharmacological treatment of tumors, or verification of proper
placement of other permanently implanted medical devices. The
rapidly growing capabilities and use of MRI in these and other
areas prevent an increasingly large group of patients from
benefiting from this powerful diagnostic and intra-operative
tool.
The use of implantable medical devices is well known in the prior
art. Thus, e.g., U.S. Pat. No. 4,180,600 discloses and claims an
implantable medical device comprising a shielded conductor wire
consisting of a conductive copper core and a magnetically soft
alloy metallic sheath metallurgically secured to the conductive
core, wherein the sheath consists essentially of from 2 to 5 weight
percent of molybdenum, from about 15 to about 23 weight percent of
iron, and from about 75 to about 85 weight percent of nickel.
Although the device of this patent does provide magnetic shielding,
it still creates heat when it interacts with strong magnetic
fields, and it can still disrupt and distort magnetic resonance
images.
Thus, e.g., U.S. Pat. No. 5,817,017 discloses and claims an
implantable medical device having enhanced magnetic image
visibility. The magnetic images are produced by known magnetic
imaging techniques, such as MRI. The invention disclosed in the
'017 patent is useful for modifying conventional catheters, stents,
guide wires and other implantable devices, as well as
interventional devices, such as for suturing, biopsy, which devices
may be temporarily inserted into the body lumen or tissue; and it
is also useful for permanently implantable devices.
As is disclosed in the '017 patent, paramagnetic ionic particles
are fixedly incorporated and dispersed in selective portions of an
implantable medical device such as, e.g., a catheter. When the
catheter coated with paramagnetic ionic particles is inserted into
a patient undergoing magnetic resonance imaging, the image signal
produced by the catheter is of higher intensity. However,
paramagnetic implants, although less susceptible to magnetization
than ferromagnetic implants, can produce image artifacts in the
presence of a strong magnetic field, such as that of a magnetic
resonant imaging coil, due to eddy currents generated in the
implants by time-varying electromagnetic fields that, in turn,
disrupt the local magnetic field and disrupt the image.
Any electrically conductive material, even a non-metallic material,
and even if not in an electrical circuit, will develop eddy
currents and thus produce electrical potential and thermal heating
in the presence of a time-varying electromagnetic field or a radio
frequency field.
Thus, there is a need to provide an implantable medical device,
which is shielded from strong electromagnetic fields, which does
not create large amounts of heat in the presence of such fields,
and which does not produce image artifacts when subjected to such
fields. It is one object of the present invention to provide such a
device, including a shielding device that can be reversibly
attached to an implantable medical device.
FIGS. 8A, 8B, 8C, and 8D are schematic sectional views of a
substrate 201, which is preferably a part of an implantable medical
device.
Referring to FIG. 8A, it will be seen that substrate 201 is coated
with nanomagnetic particles 202 on the exterior surface 203 of the
substrate.
Referring to FIG. 8B, and in the embodiment depicted therein, the
substrate 201 is coated with nanomagnetic particulate 202 on both
the exterior surface 203 and the interior surface 204.
Referring to FIG. 8C, and in the preferred embodiment depicted
therein, a layer of insulating material 205 separates substrate 201
and the layer of nanomagnetic coating 202.
Referring to FIG. 8D, it will be seen that one or more layers of
insulating material 205 separate the inside and outside surfaces of
substrate 201 from respective layers of nanomagnetic coating
202.
FIG. 9 is a schematic sectional view of a substrate 301 which is
part of an implantable medical device (not shown). Referring to
FIG. 9, and in the embodiment depicted therein, it will be seen
that substrate 301 is coated with nanomagnetic material 302, which
may differ from nanomagnetic material 202.
In one embodiment, the substrate 301 is in the shape of a cylinder,
such as an enclosure for a medical catheter, stent, guide wire, and
the like. In one aspect of this embodiment, the cylindrical
substrate 301 encloses a helical member 303, which is also coated
with nanomagnetic particulate material 302.
In another embodiment (not shown), the cylindrical substrate 301
depicted in FIG. 9 is coated with multiple layers of nanomagnetic
materials. In one aspect of this embodiment, the multiple layers of
nanomagnetic particulate are insulated from each other. In another
aspect of this embodiment, each of such multiple layers is
comprised of nanomagnetic particles of different sizes and/or
densities and/or chemical densities. In one aspect of this
embodiment, not shown, each of such multiple layers may have
different thickness. In another aspect of this embodiment, the
frequency response and degree of shielding of each such layer
differ from that of one or more of the other such layers.
FIG. 10 is a flow diagram of a preferred process of the invention.
In FIG. 2, reference is made to one or more conductors as being the
substrate(s); it is to be understood, however, that other
substrate(s) material(s) and/or configurations also may be
used.
In the first step of this process depicted in FIG. 10, step 240,
the substrate 201 (see FIG. 8A) is coated with electrical
insulative material. Suitable insulative materials include
nano-sized silicon dioxide, aluminum oxide, cerium oxide,
yttrium-stabilized zirconium, silicon carbide, silicon nitride,
aluminum nitride, and the like. In general, these nano-sized
particles will have a particle distribution such that at least 90
weight percent of the particles have a dimension in the range of
from about 10 to about 100 nanometers.
The coated substrate 201 may be prepared by conventional means such
as, e.g., the process described in U.S. Pat. No. 5,540,959, the
entire disclosure of which is incorporated by reference into this
specification. This patent describes and claims a process for
preparing a coated substrate, comprising the steps of: (a) creating
mist particles from a liquid, wherein: 1. said liquid is selected
from the group consisting of a solution, a slurry, and mixtures
thereof, 2. said liquid is comprised of solvent and from 0.1 to 75
grams of solid material per liter of solvent, 3. at least 95 volume
percent of said mist particles have a maximum dimension less than
100 microns, and 4. said mist particles are created from said first
liquid at a rate of from 0.1 to 30 milliliters of liquid per
minute; (b) contacting said mist particles with a carrier gas at a
pressure of from 761 to 810 millimeters of mercury; (c) thereafter
contacting said mist particles with alternating current radio
frequency energy with a frequency of at least 1 megahertz and a
power of at least 3 kilowatts while heating said mist to a
temperature of at least 100 degree centigrade, thereby producing a
heated vapor; (d) depositing said heated vapor onto a substrate,
thereby producing a coated substrate; and (e) subjecting said
coated substrate to a temperature of from about 450 to about 1,400
degree centigrade for at least 10 minutes.
By way of further illustration, one may coat substrate 201 by means
of the process disclosed in a text by D. Satas on "Coatings
Technology Handbook" (Marcel Dekker, Inc., New York, 1991). As is
disclosed in such text, one may use cathodic arc plasma deposition
(see pages 229 et seq.), chemical vapor deposition (see pages 257
et seq.), sol-gel coatings (see pages 655 et seq.), and the
like.
Referring again to FIGS. 8C and 8D, and by way of illustration and
not limitation, these Figures are sectional views of the coated
substrate 201. It will be seen that, in the embodiments depicted,
insulating material 205 separates the substrate and the layer of
nanomagnetic material 202. In order to obtain the structure
depicted in FIGS. 8C and 8D, one may first coat the substrate with
insulating material 205, and then apply a coat of nanomagnetic
material 202 on top of the insulating material 205; see, e.g., step
248 of FIG. 10.
The insulating material 205 that is disposed between substrate 201
and the layer of nanomagnetic coating 202 preferably has an
electrical resistivity of from about 1,000,000,000 to about
10,000,000,000,000 ohm-centimeter.
After the insulating material 205 has been deposited, and in one
preferred embodiment, the coated substrate is heat-treated in step
250 of FIG. 10. The heat treatment often is preferably used in
conjunction with coating processes in which heat is required to
bond the insulative material to the substrate 201.
The heat-treatment step 250 may be conducted after the deposition
of the insulating material 205, or it may be conducted
simultaneously therewith. In either event, and when it is used, it
is preferred to heat the coated substrate 201 to a temperature of
from about 200 to about 600 degree Centigrade for about 1 minute to
about 10 minutes.
Referring again to FIG. 10, and in step 252 of the process, after
the coated substrate 201 has been subjected to heat treatment step
250, the substrate is allowed to cool to a temperature of from
about 30 to about 100 degree Centigrade over a period of time of
from about 3 to about 15 minutes.
One need not invariably heat-treat and/or cool. Thus, referring to
FIG. 10, one may immediately coat nanomagnetic particulate onto the
coated substrate in step 254, after step 248 and/or after step 250
and/or after step 252.
In step 254, nanomagnetic material(s) are coated onto the
previously coated substrate 201. This is best shown in FIGS. 8C and
8D, wherein the nanomagnetic materials are identified as 202.
Nanomagnetic material is magnetic material which has an average
particle size less than 100 nanometers and, preferably, in the
range of from about 2 to about 50 nanometers. Reference may be had,
e.g., to U.S. Pat. No. 5,889,091 (Rotationally Free Nanomagnetic
Material), U.S. Pat. Nos. 5,714,136, 5,667,924, and the like. The
entire disclosure of each of these United States patents is hereby
incorporated by reference into this specification.
The nanomagnetic material may be, e.g., nano-sized ferrites such
as, e.g., the nanomagnetic ferrites disclosed in U.S. Pat. No.
5,213,851, the entire disclosure of which is hereby incorporated by
reference into this specification. This patent discloses and claim
a process for coating a layer of ferrite material with a thickness
of from about 0.1 to about 500 microns onto a substrate at a
deposition rate of from about 0.01 to about 10 microns per minute
per 35 square centimeters of substrate surface, comprising the
steps of: (a) providing a solution comprised of a first compound
and a second compound, wherein said first compound is an iron
compound and said second compound is selected from the group
consisting of compound of nickel, zinc, magnesium, strontium,
barium, manganese, lithium, lanthanum, yttrium, scandium, samarium,
europium, terbium, dysprosium, holmium, erbium, ytterbium,
lutetium, cerium, praseodymium, thulium, neodymium, gadolinium,
aluminum, iridium, lead, chromium, gallium, indium, cobalt,
titanium, and mixtures thereof, and wherein said solution is
comprised of from about 0.01 to about 1 kilogram of a mixture
consisting essentially of said compounds per liter of said
solution; (b) subjecting said solution to ultrasonic sound waves at
a frequency in excess of 20 kilohertz, and to an atmospheric
pressure of at least about 600 millimeters of mercury, thereby
causing said solution to form into an aerosol; (c) providing a
radio frequency plasma reactor comprised of a top section, a bottom
section, and a radio frequency coil; (d) generating a hot plasma
gas within said radio frequency plasma reactor, thereby producing a
plasma region; (e) providing a flame region disposed above said top
section of said radio frequency plasma reactor; (f) contacting said
aerosol with said hot plasma gas within said plasma reactor while
subjecting said aerosol to an atmospheric pressure of at least 600
millimeters of mercury, and to a radio frequency alternating
current at a frequency of from about 100 kilohertz to about 30
megahertz, thereby forming a vapor; (g) providing a substrate
disposed above said flame region; and (h) contacting said vapor
with said substrate, thereby forming said layer of ferrite
material.
By way of further illustration, one may use the techniques
described in an article by M. De Marco, X. W. Wang, et al. on
"Mossbauer and Magnetization Studies of Nickel Ferrites", published
in the Journal of Applied Physics 73(10), May 15, 1993, at pages
6287-6289.
In general, the thickness of the layer of nanomagnetic material
deposited onto the coated substrate 201 is from about 100
nanometers to about 10 micrometers and, more preferably, from about
0.1 to 3 microns.
Referring again to FIG. 10, after the nanomagnetic material is
coated in step 254, the coated substrate may be heat-treated in
step 256. In this optional step 256, it is preferred to subject the
coated substrate 201 to a temperature of from about 200 to about
600 degree Centigrade for from about 1 to about 10 minutes.
In one embodiment (not shown) additional insulating layers may be
coated onto the substrate 201, by one or more of the processes
disclosed hereinabove; see, e.g., optional step 258 of FIG. 10.
Without wishing to be bound to any particular theory, the
applicants believe that the nanomagnetic particles 202 trap and pin
magnetic lines of flux impinging on substrate 201, while at the
same time minimizing or eliminating the flow of electrical currents
through the coating and/or substrate.
In order to function optimally, the nanomagnetic material(s) 202
preferably have a specified magnetization. As is know to those
skilled in the art, magnetization is the magnetic moment per unit
volume of a substance. Reference may be had, e.g., to U.S. Pat.
Nos. 4,169,998, 4,168,481, 4,166,263, 5,260,132, 4,778,714, and the
like. The entire disclosure of each of these United States patents
is hereby incorporated by reference into this specification.
Referring again to FIGS. 8A, 8B, 8C, and 8D, the layer of
nanomagnetic particles 202 preferably has a saturation
magnetization, at 25 degree Centigrade, of from about 1 to about
36,000 Gauss. and preferably from about 1 to about 26,000 Gauss. In
one embodiment, the saturation magnetization at room temperature of
the nanomagnetic particles is from about 500 to about 10,000 Gauss.
For a discussion of the saturation magnetization of various
materials, reference may be had, e.g., to U.S. Pat. Nos. 4,705,613,
4,631,613, 5,543,070, 4,901,741 (cobalt, samarium, and gadolinium
alloys), and the like. The entire disclosure of each of these
United States patents is hereby incorporated by reference into this
specification. As will be apparent to those skilled in the art,
especially upon studying the aforementioned patents, the saturation
magnetization of thin films is often higher than the saturation
magnetization of bulk objects.
In one embodiment, it is preferred to utilize a thin film with a
thickness of less than about 2 microns and a saturation
magnetization in excess of 20,000 Gauss. The thickness of the layer
of nanomagnetic material is measured from the bottom surface of
such layer that contains such material to the top surface of such
layer that contain such material; and such bottom surface and/or
such top surface may be contiguous with other layers of material
(such as insulating material) that do not contain nanomagnetic
particles. Thus, e.g., one may make a thin film in accordance with
the procedure described at page 156 of Nature, Volume 407, Sep. 14,
2000, that describes a multiplayer thin film that has a saturation
magnetization of 24,000 Gauss.
By the appropriate selection of nanomagnetic particles, and the
thickness of the film deposited, one may obtain saturation
magnetizations of as high as at least about 36,000 Gauss.
In the preferred embodiment depicted in FIG. 8A, the nanomagnetic
material 202 may be disposed within an insulating matrix (not
shown) so that any heat produced by such particles will be slowly
dispersed within such matrix. Such matrix, as indicated
hereinabove, may be made from ceria, calcium oxide, silica,
alumina, and the like. In general, the insulating material 202
preferably has a thermal conductivity of less than about 20
(calories centimeters/square centimeters-degree
second).times.10,000. See, e.g., page E-6 of the .sub.63 rd.
Edition of the "Handbook of Chemistry and Physics" (CRC Press, Inc.
Boca Raton, Fla., 1982).
The nanomagnetic material 202 typically comprises one or more of
iron, cobalt, nickel, gadolinium, and samarium atoms. Thus, e.g.,
typical nanomagnetic materials include alloys of iron, and nickel
(permalloy), cobalt, niobium and zirconium (CNZ), iron, boron, and
nitrogen, cobalt, iron, boron and silica, iron, cobalt, boron, and
fluoride, and the like. These and other materials are described in
a book by J. Douglass Adam et al. entitled "Handbook of Thin Film
Devices" (Academic Press, San Diego, Calif., 2000). Chapter 5 of
this book beginning at page 185 describes "magnetic films for
planar inductive components and devices;" and Tables 5.1. and 5.2
in this chapter describes many magnetic materials.
Some of the devices described in this application are substantially
flexible. As used in this specification, the term flexible refers
to an assembly that can be bent to form a circle with a radius of
less than 2 centimeters without braking. Put another way, the bend
radius of the coated assembly can be less than 2 centimeters.
Reference may be had, e.g., to U.S. Pat. Nos. 4,705,353, 5,946,439,
5,315,365, 4,641,917, 5,913,005, and the like. The entire
disclosure of each of these United States patents is hereby
incorporated by reference into this specification.
Some of the devices described in this specification are
substantially rigid. One such device is a rigid sheath that is
adapted to be placed over an endoscope or biopsy probe used
inter-operatively with magnetic resonance imaging.
As will be apparent, even when the magnetic insulating properties
of the assembly of this invention are not absolutely effective, the
assembly still reduces the amount of electromagnetic energy that is
transferred to the coated substrate, prevents the rapid dissipation
of heat to bodily tissue, and minimization of disruption to the
magnetic resonance image.
FIG. 11 is a schematic sectional view of a substrate 401, which is
part of an implantable medical device (not shown). Referring to
FIG. 11, and in the preferred embodiment depicted therein, it will
be seen that substrate 401 is coated with a layer 404 of
nanomagnetic material(s). The layer 404, in the embodiment
depicted, is comprised of nanomagnetic particulate 405 and
nanomagnetic particulate 406. Each of the nanomagnetic particulate
405 and nanomagnetic particulate 406 preferably has an elongated
shape, with a length that is greater than its diameter. In one
aspect of this embodiment, nanomagnetic particles 405 have a
different size than nanomagnetic particles 406. In another aspect
of this embodiment, nanomagnetic particles 405 have different
magnetic properties than nanomagnetic particles 406. Referring
again to FIG. 11, and in the preferred embodiment depicted therein,
nanomagnetic particulate material 405 and nanomagnetic particulate
material 406 are designed to respond to an static or time-varying
electromagnetic fields or effects in a manner similar to that of
liquid crystal display (LCD) materials. More specifically, these
nanomagnetic particulate materials 405 and nanomagnetic particulate
materials 406 are designed to shift alignment and to effect
switching from a magnetic shielding orientation to a non-magnetic
shielding orientation. As will be apparent, the magnetic shield
provided by layer 404, can be turned "ON" and "OFF" upon demand. In
yet another embodiment (not shown), the magnetic shield is turned
on when heating of the shielded object is detected.
FIG. 12 is a schematic sectional view of substrate 501, which is
part of an implantable medical device (not shown). Referring to
FIG. 12, and to the embodiment depicted therein, it will be seen
that substrate 501 is coated with nanomagnetic particulate material
502 which may differ from particulate material 202 and/or
particulate material 302. In the embodiment depicted in FIG. 12,
the substrate 501 may be a cylinder, such as an enclosure for a
catheter, medical stent, guide wire, and the like. The assembly
depicted in FIG. 12 includes a channel 508 located on the periphery
of the medical device. An actively circulating, heat-dissipating
fluid (not shown) can be pumped into channel 508 through port 507,
and exit channel 508 through port 509. The heat-dissipation fluid
(not shown) will draw heat to another region of the device,
including regions located outside of the body where the heat can be
dissipated at a faster rate. In the embodiment depicted, the
heat-dissipating flow flows internally to the layer of nanomagnetic
particles 502.
In another embodiment, not shown, the heat dissipating fluid flows
externally to the layer of nanomagnetic particulate material
502.
In another embodiment (not shown), one or more additional polymer
layers (not shown) are coated on top of the layer of nomagnetic
particulate 502. In one aspect of this embodiment, a high thermal
conductivity polymer layer is coated immediately over the layer of
nanomagnetic particulate 502; and a low thermal conductivity
polymer layer is coated over the high thermal conductivity polymer
layer. It is preferred that neither the high thermal conductivity
polymer layer nor the low thermal conductivity polymer layer be
electrically or magnetically conductive. In the event of the
occurrence of "hot spots" on the surface of the medical device,
heat from the localized "hot spots" will be conducted along the
entire length of the device before moving radially outward through
the insulating outer layer. Thus, heat is distributed more
uniformly.
Many different devices advantageously incorporate the nanomagnetic
film of this invention. In the following section of the
specification, various additional devices that incorporate the such
film are described.
The disclosure in the following section of the specification
relates generally to an implantable medical device that is immune
or hardened to electromagnetic insult or interference. More
particularly, the invention is directed to implantable medical
devices that are not part of an electrical circuit, and that
utilize shielding to harden or make these devices immune from
electromagnetic insult (i.e. minimize or eliminate the amount of
electromagnetic energy transferred to the device), namely magnetic
resonance imaging (MRI) insult
Magnetic resonance imaging (MRI) has been developed as an imaging
technique to obtain images of anatomical features of human patients
as well as some aspects of the functional activities of biological
tissue; reference may be had, e.g., to John D. Enderle's
"Introduction to Biomedical Engineering", Academic Press, San
Diego, Calif., 2000 and, in particular, pages 783-841 thereof.
Reference may also be had to Joseph D. Bronzino's "The Biomedical
Engineering Handbook", CRC Press, Boca Raton, Fla., 1995, and in
particular pages 1006-1045 thereof. These images have medical
diagnostic value in determining the state of the health of the
tissue examined.
In an MRI process, a patient is typically aligned to place the
portion of the patient's anatomy to be examined in the imaging
volume of the MRI apparatus. Such a MRI apparatus typically
comprises a primary magnet for supplying a constant magnetic field,
Bo, which is typically of from about 0.5 to about 10.0 Tesla, and
by convention, is along the z-axis and is substantially homogenous
over the imaging volume, and secondary magnets that can provide
magnetic field gradients along each of the three principal
Cartesian axis in space (generally x, y, and z or x1, x2, and x3,
respectively). A magnetic field gradient refers to the variation of
the field along the direction parallel to Bo with respect to each
of the three principal Cartesian Axis. The apparatus also comprises
one or more radio frequency (RF) coils, which provide excitation
for and detection of the MRI signal. The RF excitation signal is an
electromagnetic wave with an electrical field E and magnetic field
B1, and is typically transmitted at frequencies of 3-100
megahertz.
The use of the MRI process with patients who have implanted medical
assist devices, such as guide wires, catheters, or stents, often
presents problems. These implantable devices are sensitive to a
variety of forms of electromagnetic interference (EMI), because the
aforementioned devices contain metallic parts that can receive
energy from the very intensive EMI fields used in magnetic
resonance imaging. The above-mentioned devices may also contain
sensing and logic and control systems that respond to low-level
electrical signals emanating from the monitored tissue region of
the patient. Since these implanted devices are responsive to
changes in local electromagnetic fields, the implanted devices are
vulnerable to sources of electromagnetic noise. The implanted
devices interact with the time-varying radio-frequency (RF)
magnetic field (B1), which are emitted during the MRI procedure.
This interaction can result in damage to the implantable device, or
it can result in heating of the device, which in turn can harm the
patient or physician using the device. This interaction can also
result in degradation of the quality of the image obtained by the
MRI process.
Signal loss and disruption of a magnetic resonance image can be
caused by disruption of the local magnetic field, which perturbs
the relationship between position and image, which are crucial for
proper image reconstruction. More specifically, the spatial
encoding of the MRI signal provided by the linear magnetic field
can be disrupted, making image reconstruction difficult or
impossible. The relative amount of artifact seen on an MR image due
to signal disruption is dependent upon such factors as the magnetic
susceptibility of the materials used in the implantable medical
device, as well as the shape, orientation, and position of the
medical device within the body of the patient, which is very often
difficult to control.
All non-permanently magnetized materials have non-zero magnetic
susceptibilities and are to some extent magnetic. Materials with
positive magnetic susceptibilities less than approximately 0.01 are
referred to as paramagnetic and are not overly responsive to an
applied magnetic field. They are often considered non-magnetic.
Materials with magnetic susceptibilities greater than 0.01 are
referred to as ferromagnetic. These materials can respond very
strongly to an applied magnetic field and are also referred as soft
magnets as their properties do not manifest until exposed to an
external magnetic field.
Paramagnetic materials (e.g. titanium), are frequently used to
encapsulate and shield and protect implantable medical devices due
to their low magnetic susceptibilities. These enclosures operate by
deflecting electromagnetic fields. However, although paramagnetic
materials are less susceptible to magnetization than ferromagnetic
materials, they can also produce image artifacts due to eddy
currents generated in the implanted medical device by externally
applied magnetic fields, such as the radio frequency fields used in
the MRI procedures. These eddy currents produce localized magnetic
fields, which disrupt and distort the magnetic resonance image.
Furthermore, the implanted medical device shape, orientation, and
position within the body make it difficult to control image
distortion due to eddy currents induced by the RF fields during MRI
procedures. Also, since the paramagnetic materials are electrically
conductive, the eddy currents produced in them can result in ohmic
heating and injury to the patient. The voltages induced in the
paramagnetic materials can also damage the medical device,
adversely interact with the operation of the device. Typical
adverse effects can include improper stimulation of internal
tissues and organs, damage to the medical device (melting of
implantable catheters while in the MR coil have been reported in
the literature), and/or injury to the patient.
Thus, it is desirable to provide protection against electromagnetic
interference, and to also provide fail-safe protection against
radiation produced by magnetic-resonance imaging procedures.
Moreover, it is desirable to provide devices that prevent the
possible damage that can be done at the tissue interface due to
induced electrical signals and due to thermal tissue damage.
Furthermore, it is desirable to provide devices that do not
interact with RF fields which are emitted during magnetic-resonance
imaging procedures and which result in degradation of the quality
of the images obtained during the MRI process.
In one embodiment, there is provided a coating of nanomagnetic
particles that consists of a mixture of aluminum oxide (AlO3),
iron, and other particles that have the ability to deflect
electromagnetic fields while remaining electrically non-conductive.
Preferably the particle size in such a coating is approximately 10
nanometers. Preferably the particle packing density is relatively
low so as to minimize electrical conductivity. Such a coating when
placed on a fully or partially metallic object (such as a guide
wire, catheter, stent, and the like) is capable of deflecting
electromagnetic fields, thereby protecting sensitive internal
components, while also preventing the formation of eddy currents in
the metallic object or coating. The absence of eddy currents in a
metallic medical device provides several advantages, to wit: (1)
reduction or elimination of heating, (2) reduction or elimination
of electrical voltages which can damage the device and/or
inappropriately stimulate internal tissues and organs, and (3)
reduction or elimination of disruption and distortion of a
magnetic-resonance image.
FIG. 13 is a schematic view of a catheter assembly 600 similar to
the assembly depicted in FIG. 2 of U.S. Pat. No. 3,995,623; the
entire disclosure of such patent is hereby incorporated by
reference into this specification. Referring to FIG. 6 of such
patent, it will be seen that catheter tube 625 contains multiple
lumens 603, 611, 613, and 615, which can be used for various
functions such as inflating balloons, enabling electrical
conductors to communicate with the distal end of the catheter, etc.
While four lumens are shown, it is to be understood that this
invention applies to a catheter with any number of lumens.
The similar catheter disclosed and claimed in U.S. Pat. No.
3,995,623 may be shielded by coating it in whole or in part with a
coating of nanomagnetic particulate, in any of the following
manners:
In FIG. 13A, a nanomagnetic material 650 is applied to either the
interior wall 650a or exterior wall 650b of lumens 603, 611, 613,
and 615, or imbibed 650c into the walls of these lumens within
catheter 625, or any combination of these locations.
In FIG. 13B, a nanomagnetic material 650 is applied to the interior
walls 650d of multiple lumens within a single catheter 625 or the
common exterior wall 650b or imbibed 650c into the common wall.
In FIG. 13C, a nanomagnetic material 650 is applied to the
mesh-like material 636 used within the wall of catheter 625 to give
it desired mechanical properties.
In another embodiment (not shown) a sheath coated with nanomagnetic
material on its internal surface, exterior surface, or imbibed into
the wall of sheath is placed over the catheter to shield it from
electromagnetic interference. In this manner, existing catheters
can be made MRI safe and compatible. The modified catheter assembly
thus produced is resistant to electromagnetic radiation.
FIGS. 14A through 14G are schematic views of a catheter assembly
consisting of multiple concentric elements. While two elements are
shown; 720 and 722, it is to be understood that any number of
over-lapping elements may be used, either concentrically or
planarly positioned with respect to each other.
Referring to FIGS. 14A-14G, it will be seen that catheter assembly
700 comprises an elongated tubular construction having a single,
central or axial lumen 710. The exterior catheter body 722 and
concentrically positioned internal catheter body 720 with internal
lumen 712 are preferably flexible, i.e., bendable, but
substantially noncompressible along its length. The catheter bodies
720 and 722 may be made of any suitable material. A presently
preferred construction comprises an outer wall 722 and inner wall
720 made of a polyurethane, silicone, or nylon. The outer wall 722
preferably comprises an imbedded braided mesh of stainless steel or
the like to increase torsional stiffness of the catheter assembly
700 so that, when a control handle, not shown, is rotated, the tip
sectionally of the catheter will rotate in corresponding manner.
The catheter assembly 700 may be shielded by coating it in whole or
in part with a coating of nanomagnetic particulate, in any one or
more of the following manners:
Referring to FIG. 14A, a nanomagnetic material may be coated on the
outside surface of the inner concentrically positioned catheter
body 720.
Referring to FIG. 14B, a nanomagnetic material may be coated on the
inside surface of the inner concentrically positioned catheter body
720.
Referring to FIG. 14C, a nanomagnetic material may be imbibed into
the walls of the inner concentrically positioned catheter body 720
and externally positioned catheter body 722. Although not shown, a
nanomagnetic material may be imbibed solely into either inner
concentrically positioned catheter body 720 or externally
positioned catheter body 722.
Referring to FIG. 14D, a nanomagnetic material may be coated onto
the exterior wall of the inner concentrically positioned catheter
body 720 and external catheter body 722.
Referring to FIG. 14E, a nanomagnetic material may be coated onto
the interior wall of the inner concentrically positioned catheter
body 720 and externally wall of externally positioned catheter body
722.
Referring to FIG. 14F, a nanomagnetic material may be coated on the
outside surface of the externally positioned catheter body 722.
Referring to FIG. 14G, a nanomagnetic material may be coated onto
the exterior surface of an internally positioned solid element
727.
By way of further illustration, one may apply nanomagnetic
particulate material to one or more of the catheter assemblies
disclosed and claimed in U.S. Pat. Nos. 5,178,803, 5,041,083,
6,283,959, 6,270,477, 6,258,080, 6,248,092, 6,238,408, 6,208,881,
6,190,379, 6,171,295, 6,117,064, 6,019,736, 6,017,338, 5,964,757,
5,853,394, and 6,235,024, the entire disclosure of which is hereby
incorporated by reference into this specification. The catheters
assemblies disclosed and claimed in the above-mentioned United
States patents may be shielded by coating them in whole or in part
with a coating of nanomagmetic particulate. The modified catheter
assemblies thus produced are resistant to electromagnetic
radiation.
FIGS. 15A, 15B, and 15C are schematic views of a guide wire
assembly 800 for insertion into vascular vessel (not shown), and it
is similar to the assembly depicted in U.S. Pat. No. 5,460,187, the
entire disclosure of such patent is incorporated by reference into
this specification. Referring to FIG. 15A, a coiled guide wire 810
is formed of a proximal section (not shown) and central support
wire 820 which terminates in hemispherical shaped tip 815. The
proximal end has a retaining device (not shown) enables the person
operating the guide wire to turn an orient the guide wire within
the vascular conduit.
The guide wire assembly may be shielded by coating it in whole or
in part with a coating of nanomagnetic particulate, in any of the
following manners:
Referring to FIG. 15A; the nanomagnetic material 650 is coated on
the exterior surface of the coiled guidewire 810.
Referring to FIG. 15B; the nanomagnetic material 650 is coated on
the exterior surface of the central support wire 820.
Referring to FIG. 15C; the nanomagnetic material 650 is coated on
all guide wire assembly components including coiled guide wire 810,
tip 815, and central support wire 820.
The modified guide wire assembly thus produced is resistant to
electromagnetic radiation.
By way of further illustration, one may coat with nanomagnetic
particulate matter the guide wire assemblies disclosed and claimed
in U.S. Pat. Nos. 5,211,183, 6,168,604, 6,093,157, 6,019,737,
6,001,068, 5,938,623, 5,797,857, 5,588,443, and 5,452,726 the
entire disclosure of which is hereby incorporated by reference into
this specification. The modified guide wire assemblies thus
produced are resistant to electromagnetic radiation.
FIGS. 16A and 16B are schematic views of a medical stent assembly
900 similar to the assembly depicted in FIG. 15 of U.S. Pat. No.
5,443,496; the entire disclosure of such patent is hereby
incorporated by reference into this specification.
Referring to FIG. 16A, a self-expanding stent 900 comprising joined
metal stent elements 962 are shown. The stent 960 also comprises a
flexible film 964. The flexible film 964 can be applied as a sheath
to the metal stent elements 962 after which the stent 960 can be
compressed, attached to a catheter, and delivered through a body
lumen to a desired location. Once in the desired location, the
stent 960 can be released from the catheter and expanded into
contact with the body lumen, where it can conform to the curvature
of the body lumen. The flexible film 964 is able to form folds,
which allow the stent elements to readily adapt to the curvature of
the body lumen. The medical stent assembly disclosed and claimed in
U.S. Pat. No. 5,443,496 may be shielded by coating it in whole or
in part with a nanomagnetic coating in any of the following
manners:
Referring to FIG. 16A, flexible film 964 may be coated with a
nanomagnetic coating on its inside or outside surfaces, or within
the film itself.
In one embodiment, a stent (not shown) is coated with a
nanomagnetic material.
It is to be understood that any one of the above embodiments may be
used independently or in conjunction with one another within a
single device.
In yet another embodiment (not shown), a sheath (not shown), coated
or imbibed with a nanomagnetic material is placed over the stent,
particularly the flexible film 964, to shield it from
electromagnetic interference. In this manner, existing stents can
be made MRI safe and compatible.
By way of illustration and not limitation, one may coat one or more
of the medical stent assemblies disclosed and claimed in U.S. Pat.
Nos. 6,315,794, 6,190,404, 5,968,091, 4,969,458, 6,342,068,
6,312,460, 6,309,412, and 6,305,436, the entire disclosure of each
of which is hereby incorporated by reference into this
specification. The medical stent assemblies disclosed and claimed
in the above-mentioned United States patents may be shielded by
coating them in whole or in part with a coating of nanomagmetic
particulate, as described above. The modified medical stent
assemblies thus produced are resistant to electromagnetic
radiation.
FIG. 17 is a schematic view of a biopsy probe assembly 1000 similar
to the assembly depicted in FIG. 1 of U.S. Pat. No. 5,005,585 the
entire disclosure of such patent is hereby incorporated by
reference into this specification.
Referring to FIG. 17, the biopsy probe assembly is composed of
three separate components, a hollow tubular cannula or needle 1001,
a solid intraluminar rod-like stylus 1002, and a clearing rod or
probe (not shown).
The components of the assembly are preferably formed of an alloy,
such as stainless steel, which is corrosion resistant and
non-toxic. Cannula 1001 has a proximal end (not shown) and a distal
end 1005 that is cut at an acute angle with respect to the
longitudinal axis of the cannula and provides an annular cutting
edge.
By way of further illustration, biopsy probe assemblies are
disclosed and claimed in U.S. Pat. Nos. 4,671,292, 5,437,283,
5,494,039, 5,398,690, and 5,335,663, the entire disclosure of each
of which is hereby incorporated by reference into this
specification. The biopsy probe assemblies disclosed and claimed in
the above-mentioned United States patents may be shielded by
coating them in whole or in part with a coating of nanomagmetic
particulate, in any of the following manners: Cannula 1001 may be
coated, intraluminar stylus 1002 may be coated, and/or the clearing
rod may be coated.
In one variation on this design (not shown), a biocompatible sheath
is placed over the coated cannula 1001 to protect the nanomagnetic
coating from abrasion and from contacting body fluids.
In one variation on this design (not shown), the biocompatible
sheath has on its interior surface or within its walls a
nanomagnetic coating.
In yet another embodiment (not shown), a sheath (not shown), coated
or imbibed with a nanomagnetic material is placed over the biopsy
probe, to shield it from electromagnetic interference. In this
manner, existing stents can be made MRI safe and compatible.
The modified biopsy probe assemblies thus produced are resistant to
electromagnetic radiation.
FIGS. 18A and 18B are schematic views of a flexible tube endoscope
assembly 1180 similar to the assembly depicted in FIG. 1 of U.S.
Pat. No. 5,058,567 the entire disclosure of such patent is hereby
incorporated by reference into this specification.
MRI is increasingly being used interoperatively to guide the
placement of medical devices such as endsocpes which are very good
at treating or examining tissues close up, but generally cannot
accurately determine where the tissues being examined are located
within the body.
Referring to FIG. 18A, the endoscope 1100 employs a flexible tube
1110 with a distally positioned objective lens 1120. Flexible tube
1110 is preferably formed in such manner that the outer side of a
spiral tube is closely covered with a braided-wire tube (not shown)
formed by weaving fine metal wires into a braid. The spiral tube is
formed using a precipitation hardening alloy material, for example,
beryllium bronze (copper-beryllium alloy).
By way of further illustration, endoscope tube assemblies are
disclosed and claimed in U.S. Pat. Nos. 4,868,015, 4,646,723,
3,739,770, 4,327,711, and 3,946,727, the entire disclosure of each
of which is hereby incorporated by reference into this
specification. The endoscope tube assemblies disclosed and claimed
in the above-mentioned United States patents may be shielded by
coating them in whole or in part with a coating of nanomagmetic
particulate, in any of the following manners:
Referring to FIG. 18A; sheath 1180 is a sheath coated with
nanomagnetic material on its inside surface 650a, exterior surface
650b, or imbibed into its structure 650c; and such sheath is placed
over the endoscope, particularly the flexible tube 1110, to shield
it from electromagnetic interference.
In yet another embodiment (not shown), flexible tube 1110 is coated
with nanomagnetic materials on its internal surface, or imbibed
with nanomagnetic materials within its wall.
In another embodiment (not shown), the braided-wire element within
flexible tube 1110 is coated with a nanomagnetic material.
In this manner, existing endoscopes can be made MRI safe and
compatible. The modified endoscope tube assemblies thus produced
are resistant to electromagnetic radiation.
FIG. 19 is a schematic illustration of a sheath assembly 2000
comprised of a sheath 2002 whose surface 2004 is comprised of a
multiplicity of nanomagnetic material 2006, 2008, and 2010. In one
embodiment, the nanomagnetic material consists of or comprises
nanomagnetic liquid crystal material. Additionally, nanomagnetic
materials 2006, 2008, and 2010 may be placed on the inside surface
of sheath 2002, imbibed into the wall of sheath 2002, or any
combination of these locations.
The sheath 2002 may be formed from electrically conductive
materials that include metals, carbon composites, carbon nanotubes,
metal-coated carbon filaments (wherein the metal may be either a
ferromagnetic material such as nickel, cobalt, or magnetic or
non-magnetic stainless steel; a paramagnetic material such as
titanium, aluminum, magnesium, copper, silver, gold, tin, or zinc;
a diamagnetic material such as bismuth, or well known
superconductor materials), metal-coated ceramic filaments (wherein
the metal may be one of the following metals: nickel, cobalt,
magnetic or non-magnetic stainless steel, titanium, aluminum,
magnesium, copper, silver, gold, tin, zinc, bismuth, or well known
superconductor materials, a composite of metal-coated carbon
filaments and a polymer (wherein the polymer may be one of the
following: polyether sulfone, silicone, polymide, polyvinylidene
fluoride, epoxy, or urethane), a composite of metal-coated ceramic
filaments and a polymer (wherein the polymer may be one of the
following: polyether sulfone, silicone, polymide, polyvinylidene
fluoride, epoxy, or urethane), a composite of metal-coated carbon
filaments and a ceramic (wherein the ceramic may be one of the
following: cement, silicates, phosphates, silicon carbide, silicon
nitride, aluminum nitride, or titanium diboride), a composite of
metal-coated ceramic filaments and a ceramic (wherein the ceramic
may be one of the following: cement, silicates, phosphates, silicon
carbide, silicon nitride, aluminum nitride, or titanium diboride),
or a composite of metal-coated (carbon or ceramic) filaments
(wherein the metal may be one of the following metals: nickel,
cobalt, magnetic or non-magnetic stainless steel, titanium,
aluminum, magnesium, copper, silver, gold, tin, zinc, bismuth, or
well known superconductor materials), and a polymer/ceramic
combination (wherein the polymer may be one of the following:
polyether sulfone, silicone, polymide, polyvinylidene fluoride, or
epoxy and the ceramic may be one of the following: cement,
silicates, phosphates, silicon carbide, silicon nitride, aluminum
nitride, or titanium diboride).
In one preferred embodiment, the sheath 2002 is comprised of at
least about 50 volume percent of the nanomagnetic material
described elsewhere in this specification.
As is known to those skilled in the art, liquid crystals are
nonisotrpic materials (that are neither crystalline nor liquid)
composed of long molecules that, when aligned, are parallel to each
other in long clusters. These materials have properties
intermediate those of crystalline solids and liquids. See, e.g.,
page 479 of George S. Brady et al.'s "Materials Handbook,"
Thirteenth Edition (McGraw-Hill, Inc., New York, 1991).
Ferromagnetic liquid crystals are known to those in the art, and
they are often referred to as FMLC. Reference may be had, e.g., to
U.S. Pat. Nos. 4,241,521, 6,451,207, 5,161,030, 6,375,330,
6,130,220, and the like. The entire disclosure of each of these
United States patents is hereby incorporated by reference into this
specification.
Reference also may be had to U.S. Pat. No. 5,825,448, which
describes a reflective liquid crystalline diffractive light valve.
The figures of this patent illustrate how the orientations of the
magnetic liquid crystal particles align in response to an applied
magnetic field.
Referring again to FIG. 19A, and in the embodiment depicted
therein, it will be seen that sheath 2002 may be disposed in whole
or in part over medical device 2012. In the embodiment depicted,
the sheath 2002 is shown as being bigger that the medical device
2012. It will be apparent that such sheath 2002 may be smaller than
the medical device 2012, may be the same size as the medical device
2012, may have a different cross-sectional shape than the medical
2012, and the like.
In one preferred embodiment, the sheath 2002 is disposed over the
medical device 2012 and caused to adhere closely thereto. One may
create this adhesion either by use of adhesive(s) and/or by
mechanical shrinkage.
In one embodiment, shrinkage of the sheath 2012 is caused by heat,
utilizing well known shrink tube technology. Reference may be had,
e.g., to U.S. Pat. Nos. 6,438,229, 6,245,053, 6,082,760, 6,055,714,
5,903,693, and the like. The entire disclosure of each of these
United States patents is hereby incorporated by reference into this
specification.
In another embodiment of the invention, the sheath 2002 is a rigid
or flexible tube formed from polytetrafluoroethylene that is heat
shrunk into resilient engagement with the implantable medical
device. The sheath can also be formed from heat shrinkable polymer
materials e.g., low density polyethylene (LDPE), linear low-density
polyethylene (LLDPE), ethylene vinyl acrylate (EVA), ethylene
methacrylate (EMA), ethylene methacrylate acid (EMAA) and ethyl
glycol methacrylic acid (EGMA). The polymer material of the heat
shrinkable sheath should have a Vicat softening point less than 50
degrees Centigrade and a melt index less than 25. A particularly
suitable polymer material for the sheath of the invention is a
copolymer of ethylene and methyl acrylate which is available under
the trademark Lotryl 24MA005 from Elf Atochem. This copolymer
contains 25% methyl acrylate, has a Vicat softening point of about
43 degree centigrade and a melt-index of about 0.5.
In another embodiment of the invention, the sheath 2002 is a
collapsible tube that can be extended over the implantable medical
device such as by unrolling or stretching.
In yet another embodiment of the invention, the sheath 2002
contains a tearable seam along its axial length, to enable the
sheath to be withdrawn and removed from the implantable device
without explanting the device or disconnecting the device from any
attachments to its proximal end, thereby enabling the
electromagnetic shield to be removed after the device is implanted
in a patient. This is a preferable feature of the sheath, since it
eliminates the need to disconnect any devices connected to the
proximal (external) end of the device, which could interrupt the
function of the implanted medical device. This feature is
particularly critical if the shield is being applied to a
life-sustaining device, such as a temporary implantable cardiac
pacemaker.
The ability of the sheath 1180 or 2002 to be easily removed, and
therefore easily disposed, without disposing of the typically much
more expensive medical device being shielded, is a preferred
feature since it prevents cross-contamination between patients
using the same medical device.
In still another embodiment of the invention, an actively
circulating, heat-dissipating fluid can be pumped into one or more
internal channels within the sheath. The heat-dissipating fluid
will draw heat to another region of the device, including regions
located outside of the body where the heat can be dissipated at a
faster rate. The heat-dissipating flow may flow internally to the
layer of nanomagnetic particles, or external to the layer of
nanomagnetic particulate material.
FIG. 19B illustrates a process 2001 in which heat 2030 is applied
to a shrink tube assembly 2003 to produce the final product 2005.
For the sake of simplicity of representation, the controller 2007
has been omitted from FIG. 19B.
Referring again to FIG. 19A, and in the preferred embodiment
depicted therein, it will be seen that a controller 2007 is
connected by switch 2009 to the sheath 2002. The controller 2007. A
multiplicity of sensors 2014 and 2016, e.g., can detect the
effectiveness of sheath 2002 by measuring, e.g., the temperature
and/or the electromagnetic field strength within the shield 2012.
One or more other sensors 2018 are adapted to measure the
properties of sheath 2012 at its exterior surface 2004.
For the particular sheath embodiment utilizing a liquid crystal
nanomagnetic particle construction, and depending upon the data
received by controller 2007, the controller 2007 may change the
shielding properties of shield 2012 by delivering electrical and/or
magnetic energy to locations 2020, 2022, 2024, etc. The choice of
the energy to be delivered, and its intensity, and its location,
and its duration, will vary depending upon the status of the sheath
2012.
In the embodiment depicted in FIG. 19, the medical device may be
moved in the direction of arrow 2026, while sheath may be moved in
the direction of arrow 2028, to produce the assembly 2001 depicted
in FIG. 19B. Thereafter, heat may be applied to this assembly to
produce the assembly 2005 depicted in FIG. 19B.
In one embodiment, not shown, the sheath 2002 is comprised of an
elongated element consisting of a proximal end and a distal end,
containing one or more internal hollow lumens, whereby the lumens
at said distal end may be open or closed, is used to temporarily or
permanently encase an implantable medical device.
In this embodiment, the elongated hollow element is similar to the
sheath disclosed and claimed in U.S. Pat. No. 5,964,730; the entire
disclosure of which is hereby incorporated by reference into this
specification.
Referring again to FIG. 19A, and in the embodiment depicted
therein, the sheath 2002 is preferably coated and/or impregnated
with nanomagnetic shielding material 2006/2008/2010 that comprises
at least 50 percent of its external surface, and/or comprises at
least 50 percent of one or more lumen internal surfaces, or imbibed
within the wall 2015 of sheath 2002, thereby protecting at least
fifty percent of the surface area of one or more of its lumens, or
any combination of these surfaces or areas, thus forming a shield
against electromagnetic interference for the encased medical
device.
FIG. 20A is a schematic of a multiplicity of liquid crystals 2034,
2036, 2038, 2040, and 2042 disposed within a matrix 2032. As will
be apparent, each of these liquid crystals is comprised of
nanomagnetic material 2006. In the configuration illustrated in
FIG. 20A, the liquid crystals 2034 et seq. are not aligned.
By comparison, in the configuration depicted in FIG. 20B, such
liquid crystals 2034 are aligned. Such alignment is caused by the
application of an external energy field (not shown).
The liquid crystals disposed within the matrix 2032 may have
different concentrations and/or compositions of nanomagnetic
particles 2006, 2009, and/or 2010; see FIG. 20C and liquid crystals
2044, 2046, 2048, 2050, and 2052. Alternatively, or additionally,
the liquid crystals may have different shapes; see FIGS. 20D, 20E,
and 20F and liquid crystals 2054 and 2056, 2058, 2060, 2062, 2064,
and 2066. As will be apparent, by varying the size, shape, number,
location, and/or composition of such liquid crystals, one may
custom design any desired response.
FIG. 21 is a graph of the response of a typical matrix 2032
comprised of nanomagnetic liquid crystals. Three different curves,
curves 2068, 2070, and 2072, are depicted, and they correspond to
the responses of three different nanomagnetic liquid crystal
materials have different shapes and/or sizes and/or
compositions.
Referring to FIG. 21, and for each of curves 2068 through 2072, it
will be seen that there is often a threshold point 2074 below which
no meaningful response to the applied magnetic field is seen; see,
e.g., the response for curve 2070.
It should be noted, however, that some materials have a low
threshold before they start to exhibit response to the applied
magnetic field; see, e.g., curve 2068. On the other hand, some
materials have a very large threshold; see, e.g., threshold 2076
for curve 2072.
One may produce any desired response curve by the proper
combination of nanomagnetic material composition, concentration,
and location as well as liquid crystal geometries, materials, and
sizes. Other such variables will be apparent to those skilled in
the art.
Referring again to FIG. 21, it will be seen that there often is a
monotonic region 2078 in which the increase of alignment of the
nanomagnetic material is monotonic and often directly proportional;
see, e.g., curve 2070.
There also is often a saturation point 2080 beyond which an
increase in the applied magnetic field does not substantially
increase the alignment.
As will be seen from the curves in FIG. 21, the process often is
reversible. One may go from a higher level of alignment to a lower
level by reducing the magnetic field applied.
The frequency of the magnetic field applied also influences the
degree of alignment. As is illustrated in FIG. 22, for one
nanomagnetic liquid crystal material (curve 2082), the response is
at a maximum at an initial frequency 2086 but then decreases to a
minimum at frequency 2088. By comparison, for another such curve
(curve 2090), the response is minimum at frequency 1086, increases
to a maximum at point 2098, and then decreases to a minimum at
point 2092.
Thus, one may influence the response of a particular nanomagnetic
liquid crystal material by varying its type of nanomagnetic
material, and/or its concentration, and/or its shape, and/or the
frequency to which it is subjected. Referring again to FIG. 19A,
one may affect the shielding effectiveness of shield 2002 by
supplying a secondary magnetic field (from controller 2007) at the
secondary frequencies which will elicit the desired shielding
effect.
FIG. 23 is a flow diagram illustrating a preferred process 2094 for
making nanomagnetic liquid crystal material.
Referring to FIG. 23, and in step 2100, the nanomagnetic material
of this invention is charged to a mixer 2102 via line 2104.
Thereafter, suspending medium is also charged to the mixer 2102 via
line 2106.
The suspending medium may be any medium in which the nanomagnetic
material is dispersible. Thus, e.g., the suspending medium may be a
gel, it may be an aqueous solution, it may be an organic solvent,
and the like. In one embodiment, the nanomagnetic material is not
soluble in the suspending medium; in this embodiment, a slurry is
produced. For the sake of simplicity of description, the use of a
polymer will be described in the rest of the process.
Referring again to FIG. 23, the slurry from mixer 2102 is charged
via line 2108 to mixer 2110. Thereafter, or simultaneously,
polymeric precursor of liquid crystal material is also charged to
mixer 2108 via line 2112.
As is known to those skilled in the art, aromatic polyesters
(liquid crystals) may b used as such polymeric precursor. These
aromatic polyesters are commercially available as, e.g., Vectra
(sold by Hoechst Celanese Engineering Plastic), Xydur (sold by
Amoco Performance Plastics), Granlar (sold by Granmont), and the
like. Reference may be had, e.g., to pages 649-650 of the
aforementioned "Materials Handbook." Reference also may be had,
e.g., to U.S. Pat. Nos. 4,738,880, 5,142,017, 5,006,402, 4,935,833,
and the like. The entire disclosure of each of these United States
patents is hereby incorporated by reference into this
specification.
Referring again to FIG. 23, the liquid crystal polymer is mixed
with the nanomagnetic particles for a time sufficient to produce a
substantially homogeneous mixture. Typically, mixing occurs from
about 5 to about 60 minutes.
The polymeric material formed in mixer 2110 then is formed into a
desired shape in former 2112. Thus, and referring to Joel Frados'
"Plastics Engineering Handbook," Fourth Edition (Van Nostrand
Reinhold Company, New York, N.Y., 1976), one may form the desired
shape by injection molding, extrusion, compression and transfer
molding, cold molding, blow molding, rotational molding, casting,
machining, joining, and the like. Other such forming procedures are
well known to those skilled in the art.
One may prepare several different nanomagnetic structures and join
them together to form a composite structure. One such composite
structure is illustrated in FIG. 24.
Referring to FIG. 24, assembly 2120 is comprised of nanomagnetic
particles 2006, 2010, and 2008 disposed in layers 2122, 2124, and
2126, respectively. In the embodiment depicted, the layers 2122,
2124, and 2126 are contiguous with each, thereby forming a
continuous assembly of nanomagnetic material, with different
concentrations and compositions thereof at different points. The
response of assembly 2120 to any particular magnetic field will
vary depending upon the location at which such response is
measured.
FIG. 25 illustrates an assembly 2130 that is similar to assembly
2120 but that contains an insulating layer 2132 disposed between
nanomagnetic layers 2134 and 2136. The assembly 2130
The insulating layer 2132 may be either electrically insulative
and/or thermally insulative.
FIG. 26 illustrates an assembly 2140 in which the response of
nanomagnetic material 2142 is sensed by sensor 2144 that, in the
embodiment depicted, is a pickup coil 2144. Data from sensor 2144
is transmitted to controller 2146. When and as appropriate,
controller 2146 may introduce electrical and/or magnetic energy
into shielding material 2142 in order to modify its response.
FIG. 27 is a schematic illustration of an assembly 2150. In the
embodiment depicted, concentric insulating layers 2152 and 2154
preferably have substantially different thermal conductivities.
Layer 2152 preferably has a thermal conductivity that is in the
range of from about 10 to about 2000 calories per hour per square
centimeter per centimeter per degree Celsius. Layer 2154 has a
thermal conductivity that is in the range of from about 0.2 to
about 10 calories per hour per square centimeter per centimeter per
degree Celsius. Layers.2152 and 2154 are designed by choice of
thermal conductivity and of layer thickness such that heat is
conducted axially along, and circumferentially around, layer 2152
at a rate that is between 10 times and 1000 times higher than in
layer 2154. Thus, in this embodiment, any heat that is generated at
any particular site or sites in one or more nanomagnetic shielding
layers will be distributed axially along the shielded element, and
circumferentially around it, before being conducted radially to
adjoining tissues. This will serve to further protect these
adjoining tissues from thermogenic damage even if there are minor
local flaws in the nanomagnetic shield.
Thus, in one embodiment of the invention, there is described a
magnetically shielded conductor assembly, that contains a
conductor, at least one layer of nanomagnetic material, a first
thermally insulating layer, and a second thermally insulating
layer. The first thermal insulating layer resides radially inward
from said second thermally insulating layer, and it has a thermal
conductivity from about 10 to about 2000 calories-centimeter per
hour per square centimeter per degree Celsius The second thermal
insulating layer has a thermal conductivity from about 0.2 to about
10 calories per hour per square centimeter per degree Celsius, and
the axial and circumferential heat conductance of the first thermal
insulating layer is at least about 10 to about 1000 times higher
than it is for said second thermal insulating layer.
In another embodiment of the invention, there is provided a
magnetically shielded conductor assembly as discussed hereinabove,
in which the first thermally insulating layer is disposed between
said conductor and said layer of nanomagnetic material, and the
second thermally insulating layer is disposed outside said layer of
nanomagnetic material
In another embodiment, there is provided a magnetically shielded
conductor assembly as discussed hereinabove wherein the first
thermally insulating layer is disposed outside the layer of
nanomagnetic material, and wherein the second thermally insulating
layer is disposed outside said first layer of thermally insulating
material.
In another embodiment, the shield is comprised of a abrasion
-resistant coating comprised of nanomagnetic material. Referring to
FIG. 28, it will be seen that shield 2170 is comprised of abrasion
resistant coating 2172 and nanomagnetic layer 2174.
* * * * *